As the demand for oil and gas has continued to increase, oil field operators have had to drill increasingly deeper wells to meet this demand. One of the elements of a drilling operation that makes such deep wells feasible is drilling fluid. Drilling fluid or “mud” is typically injected down into a drill pipe, through the drill bit and back up the borehole in the annulus formed between the borehole wall and the exterior of the drill pipe. The fluid provides drill bit lubrication and cooling, controls the borehole pressure, stabilizes the borehole wall and carries drilling cuttings up and away from the bottom of the borehole. The fluid typically flows in a closed loop, wherein the fluid is filtered to remove cuttings and other impurities before it is re-injected into the borehole.
As drilling progresses, gasses from the surrounding formation may be released into the drilling fluid, forming bubbles within the fluid. Operators will sometimes separate out the gases from the fluid to measure and analyze the hydrocarbons present in the extracted sample gas. Such separation is performed by a motor-driven drilling fluid degasser. Because of the presence of flammable gases, air motors are generally used to drive the degasser rather than more expensive explosion-proof electric motors. Such motors are typically directly mounted to the degasser in order to reduce the amount of space needed by the degasser/motor assembly, reduce the level of vibration produced by the operation of the assembly and reduce the number of assembly components.
As a result of being driven at high pressures and/or high flow rates, air motors typically leak, allowing air to escape from seals around the output shaft. These air leaks can increase if the shaft surface becomes worn due to debris or inadequate lubrication. While such leaks are considered normal for air motors, the inventors have observed that they present a significant drawback when an air motor drives a degasser. Because the motor is mounted directly to the degasser chamber, air can leak from the motor into the degasser chamber where it mixes with the extracted sample gas. This addition of an unknown quantity of air dilutes the extracted sample gas by an undetermined amount. Further, because the air used to drive an air motor is mixed with lubricating oil, additional contamination can occur and add to the error in the measurement of hydrocarbons within the gas stream. To aggravate matters even further, the direct mounting of the motor prevents operation and maintenance personnel from detecting a leak until the degasser is disassembled and the motor shaft is tested for leaks. Although these problems have long been recognized, the inherent limitations of existing degasser designs have prevented the development of viable, practical solutions.
It should be understood that the drawings and corresponding detailed description do not limit the disclosure, but on the contrary, they provide the foundation for understanding all modifications, equivalents, and alternatives falling within the scope of the appended claims.